The present invention relates to a terminal adapter and, more particularly, to a terminal adapter which can effect efficient network monitoring when a plurality of LANs (Local Area Networks) are connected to one another via a WAN (Wide Area Network).
A LAN permits efficient inter-computer communication, and to date it has been utilized in a very wide variety of fields. Meanwhile, there may arise a case in which, after establishment of a LAN, its constituent computers are increased up to a physical limit, or a case in which it is intended to make communication with a computer in a different LAN established in a separate area. In such cases, it is necessary to expand the network or connect networks using a WAN. For connecting a LAN and a WAN or connecting LANs via a WAN (which is hereinafter referred to as LAN-WAN connection), a terminal adapter is utilized.
Heretofore, this type of LAN-WAN connection is realized by using gateway unit repeaters, bridges, routers and so forth. The gateway unit is a system for connecting networks of different systems. Usually, it has a protocol including a physical layer and a transport layer or more than these layers. The protocol is based on Ethernet and TCP/IP (Transmission Control Protocol/Internet Protocol) and constituted by a number of layers such as a physical layer, a data link layer, a network layer, a transport layer and an application layer.
When the gateway unit accesses an exclusive line or a switching line, including ISDN, via a terminal adapter, it effects in advance termination of the communication protocol in the LAN and protocol transform to a serial transmission form used in the WAN. Usually, the physical layer and data link layer in the LAN communication protocol are constituted by Ethernet or token ring and the network layer is constituted by IP. As the protocol for conversion to the serial transmission form for accessing the WAN, commonly called SLIP (Serial Line IP) is used.
For the LAN-WAN connection noted above, a protocol called SNMP (Simple Network Management Protocol) is usually used for network control of the LAN and gateway unit. The SNMP prescribes a general network control system. However, the control message is exchanged on the UDP (User Datagram Protocol) which is a layer above the IP noted above. Meanwhile, the terminal adapters are used as modems, ISDN-TAs, multiplexing systems and so forth. These facilities perform network control according to such information as line signal level and signal-to-noise ratio, and they individually use peculiar network control systems not based on SNMP.
Therefore, for a LAN-WAN connection, it is necessary to operate independently a network control system for the LAN and gateway unit and a network monitoring system for the terminal adapter. This means that the network user has to use two independent control systems. Alternately, a third system is necessary, which effects collective network control by collecting information obtained from the above two control systems. Therefore, it is impossible to obtain effective management and control.